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Messages - OgreVorbis

Pages: [1] 2 3 ... 5
1
Equipment / Re: Inverted V yagi aiming up into the sky
« on: July 20, 2019, 0510 UTC »
I was thinking maybe this would be more useful on medium wave.
The optimal height above ground for a dipole is 0.6 wave, but 1/4 wave comes in pretty close.
AM broadcasting has always been hard because of the height required and the high ground losses in my area.
If I made such a yagi or log periodic on MW band, do you think it would be more effective at getting the energy into the ionosphere than just having it at the correct height?

I mean, with a standard dipole isn't a lot of energy just being absorbed into the ground?

2
Equipment / Inverted V yagi aiming up into the sky
« on: July 19, 2019, 0147 UTC »
So I'm curious why I have not seen this type of antenna before. Basically what it would be is 3 or more inverted Vs stacked on top of each other along the length of the mast. I've seen something somewhat similar with inverted Vs, but not aiming upwards. With HF, we want the signal in the ionosphere, so why not aim it up? Why do hams always aim their yagis horizontally?

And when I say aiming up, I want to be clear. I do know that hams mount horizontally and vertically which is not what I'm talking about. I mean the yagi is pointing up into the sky. I figure with a dipole, the radiation angle wouldn't be right, but with an inverted V I think it would. Plus, it is much easier to install.

3
I did some looking at the all frequencies list and I've concluded that it is either erroneous or just old. It is not completely wrong, but I wouldn't rely on it. There are a lot of stations not included in there and it lists some of the international radio stations as being in the middle of the AM broadcast band which is not at all correct. Most of this came from the original file in the archive called radio-freqs.txt.

The GOVT and Distress lists are just fine.

4
I just did some additional processing. I extracted every single HF frequency from the files and put them in two plain list files with no formatting. This is good for if someone is planning to use a frequency and they aren't sure if it is taken or not.

All Frequencies:
https://pastebin.com/X21wuhPM

Govt. Frequencies:
https://pastebin.com/cMJmT5Le

Distress Frequencies:
https://pastebin.com/E93TRH93

Now this might not have absolutely everything, but it has everything contained in the archive. If anyone has any other SW frequency lists, let me know. I'd like to make a simple master list so if someone is planning on pirating they can just be sure there is nothing at all on the frequency.

5
I've done a repack because without a mediafire account, it takes forever to download each individual file.

Here is most of the important stuff in one file: https://drive.google.com/open?id=1tKNFaoG_KETDfQ1FXNEmWoTmyC2ptWPr

Thanks for the upload. There's a lot of good stuff in there  :)

6
This is ridiculous. We have plenty of spectrum if only the FCC would open up more of it. There's all that old TV spectrum that's just sitting around. It would also be ideal because it's low VHF which travels farther. And what about all those "Land/Mobile" frequencies that no one uses anymore. Everything is clustered in the high frequencies like 2.4G right now. I heard of a plan to start a WiFi band around 800MHz, but I don't think it went anywhere.

Either way, I wish the government would just step aside and let innovation happen. The only rule should be to not interfere with another signal. Just make the punishment for that very severe. Then you can open everything up and just let business and individuals use whatever frequency they wish. You could argue that this would produce chaos, but not many are going use frequencies that they know others are using because it's just not going to work as well.

7
The RF Workbench / Re: Class D V2.0
« on: June 26, 2019, 1111 UTC »
Nice. I haven't seen that one before. I found some little heatsinks for the drivers.
I am working on modifying the board now to be more like what you did here. I dropped the inverter chip and I am going to use the inverted inputs on the drivers. I replaced the long winding traces with a long bar that extends along each of them similar to what I have on the output of the fets, just smaller. I will drive with 13.8V or 15V instead of 18V because the efficiency didn't seem any better with that and they got hotter. For the decoupling caps, I switched to SMD. When I'm done I'll post the new board.

I notice you're not using the inverted inputs yourself. Are you driving it that way, or? I know it might be a little better to use an external circuit for that to do 40% duty, but the 50% duty seems to work fine for me.
Do those drivers get hot for you at all? I'm sure it's OK to get a little hot.

8
The RF Workbench / Re: Class D V2.0
« on: June 25, 2019, 0848 UTC »
Alright, I did a lot today.

What I found out is that, redhat, you were right about those clock traces. They were reducing the efficiency a bit and rounding the waves. I cut the traces to two of the drivers and inserted the clock directly into them. The waves were much more square after that. They do a little jumping around thing when the fets are powered and I'm not sure why, but they are very square. I switched from using my DDS module and used a signal generator instead cause my DDS got fried somehow.

I removed and replaced all the drivers and identified two broken fets, so I just cut them off the board. Now it seems to be working, but these drivers still get way too hot! I had to put little metal pieces on top of them and that helped, but I have to run them at 12V. If I run them at the 18V, they still get too hot.
Stretchy, you have actually tried these drivers, right? I made sure the waves are clean and measured the gate capacitance at 250pf w/o drivers attached. With them attached, it goes up to 2uF. I don't know if that's normal.

So I could make a new board with the clock traces improved, but these drivers seem no good, so I don't know what to do next. It's weird because the amfone guy used the same driver and fet combination.

9
The RF Workbench / Re: Class D V2.0
« on: June 24, 2019, 0333 UTC »
I'm not real fond of the meandering drive clock trace.  You could wind up with a propagation delay issue where the far end fets are being turned on and off slightly after the close in fets.  This can cause an overlap issue which will hurt your efficiency.

It appears as if your using through-hole parts in dead bug style construction for your bypass capacitors and loading resistors.  Is this correct?  I would use smt chip caps and resistors for this, less stray L, better bypassing and less opportunity for noise pickup.

+-RH

I see what you mean and if I ever do another board, I will try that.
But anyway, I don't think that is causing the problem.

My mind is really blown by this problem.

I tried direct driving the FETs with a signal generator and they seem to work. I guess they could be partially damaged or something, but I hooked up each pair and despite the signal generator not giving them their full drive, each pair made about 30W at 13.5V which makes me think they are probably not busted.

The condition when the problem happens is only with input drive to the drivers regardless of if the FETs are powered or not.
I looked at the scope and the waveforms entering the drivers are a little warped, but decent (probably just my cabling). The waves coming out of the drivers are not amped though; they are much less voltage (like 1V or so). They are clearly not working right. Now is it because my circuit is wrong or something with the FETs, I don't know.

My only thought at this point is to remove all the FETs (which will kill them in the process given my design) and power the drivers with no FETs attached. I really don't see what could be wrong with them though and why almost all of them have failed even though they are new.

None of this makes much sense. I have them wired directly to the FETs with no resistor, but I see stretchy and others do the same. I am using the same combination of FET and driver also. I don't see what else there is other than I just got bad parts. I see stretchy, you put a cap in series with the input pin of the driver. Could it be that?

10
The RF Workbench / Re: Class D V2.0
« on: June 22, 2019, 2224 UTC »
Ok, not sure wtf it could be then. You can switch those FETs with 12V, however 15V is marginally better, no need to go to 18V. You have decoupled the drivers VERY closely with 100nF's?

Str.

Yep, pretty close.

Have you looked at the drive waveforms on the gates to be sure they all look similar?

I had something similar happen recently.  For some reason, one of my rf fets got zinged and the gate had a breakdown.  This was causing excessive loading on the driver.  Replacement of the fet solved the problem.

I'll check it.

Here is the actual board layout in case you see anything wrong. . .


11
The RF Workbench / Re: Class D V2.0
« on: June 22, 2019, 2157 UTC »
Since your using the on fet drivers with dual input, you could feed the clock into the inverting inputs on one half of the bridge, and non inverting input on the other.  That would allow you to eliminate the 74HCT14.

Also, depending on power, one turn through the output transformer may exceed the flux density of the material.  I would probably do a two turn primary, four turn secondary, made out of coax.  This would also help control your impedances and keep your strays down.

+-RH

OK, I'll keep that in mind.

I'm in agreement with RH + parasitics can be a real issue with high power RF.

Start with a low Voltage on the FETs and monitor with a scope. You may have to set the trigger up so you capture short duration spikes.

Very layout dependant.

Try small Res in series with FET gates.

Do you have spec ani to monitor the RF O/P? Would help as you can see naughty things beginning to happen.

Need to see some scope traces...

Str.

I do have a spectrum analyzer and scope. I think the problem is likely something more simple than parasitics. The problem happens even with no voltage applied to the FETs. Voltage applied to the drivers is fine, but as soon as I input the square waves, the two drivers begin to heat.

It would be very hard for me to add the Res in series on my board. Plus the amfone guy that this board is based on didn't do that and he claims it works. Only thing I left out are those 330 ohm resistors on the driver's inputs. Not sure if that would help.

I am running the drivers at 18V btw.

Core saturation will be easy to detect with the trapazoid method under AM conditions.  Slowly increase tone modulation until you see non-linearity start to occur and this is most likely being caused by saturation.

I'm in the process of doing the same thing to my transmitter following a change in the output topology.

+-RH

OK, good to know. I'll try that when I get there.

12
The RF Workbench / Class D V2.0
« on: June 22, 2019, 2041 UTC »
So I have finished my new design with the NCP drivers and eight SiC FETs and I tested it. I am having a bit of a problem with it. Some of the NCPs are heating up and eventually blowing out. It is not happening on a single side of the amp. I currently have only four of the eight FETs along with four drivers populated and two of the four drivers keep blowing out.

Do they need to be balanced somehow? Maybe a current limiting resistor. Right now they are just running in parallel with the 5V square wave drive.

I left out R3 - R6
Here is the schematic:

13

i'm 24 and probably come here from a different path than most of you. i'm not into amateur radio and have no interest in transmitting. i got interested in radio as part of my greater interest in the electromagnetic spectrum. i'm an astronomy major and though i have always been fascinated by the sky as a girl scout we got a visit of a grad student from the local university's astronomy program. the way she enthusiastically talked about electromagnetic waves as distant info messengers sounded like magic! from that moment on i knew what i wanted to do. she sort of became my mentor and we exchanged a lot of emails! she's now a radio astronomer and has been to some pretty exotic places like the atacama large millimeter array in chile!

i experimented for awhile and learned the rtl dongle while good for vhf and above was not the best for HF so i bought an sdrplay rsp1a from ham radio outlet about a month ago. it was a definite upgrade and so now i'm looking to upgrade my antenna. i don't have a lot of space and learned there are some compact antennas like the mini whip and magnetic loops (maybe too expensive for me on a student budget). most of all i want to take down the wire in the house lol so any advice on how to replace it would be great. there is space to mount a compact antenna outside so that is my next step.

on a personal note i was reluctant to post here as most of the people here are old enough to be my dad or in many cases grand dad and i hadn't come across another female but i at least found a thread with some people closer to my age.

btw: we dont just listen to lady gaga and justin bieber, most of us listen to everything and have tons of spotify and/or pandora playlists.  don't hate me cause i like ariana grande and charlie puth ;)

My family has a background in astronomy and my dad's first major project was building an observatory for a university. I am into radio purely because of it's interesting properties. I've thought about connecting the two areas, but I'm more concentrated on my HF projects now.

Anyway, it really depends on exactly how much space you have, but a full size antenna is always best. There really is no good way of cheating the system and making something smaller that works better. You may find something decent, but not better.

It's fun to take advantage of the surrounding resources in a clever way. Like for example if there is a large metal fence or water main, you can use that for grounding a 1/4 wave vertical. Using a slingshot or crossbow to launch fishing line into a tree and then raising the antenna with that is another way.

If you don't have any grounding resources, then my opinion is to go for an inverted V. The cable goes up a tree to a branch and the two lengths of antenna slope down to the ground (it's a sloping version of a dipole.)

Good luck and don't feel intimidated to come back :)

14
Equipment / Looking to upgrade - SDR or traditional?
« on: June 15, 2019, 1038 UTC »
So I spend most my time building and experimenting with shortwave transmitters, but so far my experience in the receiver department has been limited. I currently have two receivers. The Tecsun PL-360 and this Chinese SDR: https://www.ebay.com/itm/RTL2832U-R820T2-chip-Set-100KHz-1-7GHz-UpConverter-HF-UHF-VHF-RTL-SDR-Receiver/132465613216

I'm looking for something with very good receive sensitivity. I am not sure whether I want a traditional radio or a better SDR. It is nice to have that spectrum analyzer type view, but my main focus is on sensitivity. I am not looking to spend very much < $300.

The Airspy HF Discovery looks good. What would you recommend?
How does an SDR perform compared to a Double or Triple conversion superhet?

These traditional receivers look good, but they are a little above my price point: Alinco DX-R8T or ICOM IC-R75

15
The RF Workbench / Re: Simple SiC TX
« on: June 15, 2019, 0524 UTC »
Same ones I'm currently using, C2M0080120D's and C2M0045170D's.  Of course its all theory until you build one... 

A big part of the problem in getting above 1KW is the thermal management.  Large bonded fin heatsinks and fan capacities over 200CFM become mandatory, especially for gear meant to survive operation in outdoor summer conditions.

It will be quite the feat when it is running.

+-RH

https://www.fischerelektronik.de/web_fischer/en_US/K%C3%BChlk%C3%B6rper/D/L%C3%BCfteraggregate/index.xhtml

These are a bit pricey, but it's a good company and they have everything.

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